Thin film transistors (TFTs) are utilized in various devices, such as a liquid crystal displays, static random access memories (SRAMs) and in nonvolatile memories. Conventional TFTs have a structure that is similar to conventional bulk metal oxide semiconductor field effect transistors (MOSFETs), except that TFTs are formed in a semiconductor layer that is located above an insulating substrate, such as a glass substrate or a semiconductor substrate that is covered by an insulating layer. The TFT device density on the substrate is usually lower than desired. The decreased device density increases the device cost, since fewer devices can be made on each substrate. PCT published application WO 02/15277 A2, which corresponds to U.S. application Ser. No. 09/927,648 filed on Aug. 13, 2002, incorporated herein by reference in its entirety, describes how three dimensional rail stack arrays of TFTs may be used utilized to decrease device density.